The present invention relates to novel copolymers of alpha-olefins. More specifically, it relates to novel copolymers of ethylene with other alpha-olefins comprised of segmented copolymer chains with compositions which are intramolecularly heterogeneous and intermolecularly homogeneous, as well as to a process for making these copolymers and their use in lube oil applications.
For convenience, certain terms that are repeated throughout the present specification are defined below:
a. Inter-CD defines the compositional variation, in terms of ethylene content, among polymer chains. It is expressed as the minimum deviation (analogous to a standard deviation) in terms of weight percent ethylene, from the average ethylene composition for a given copolymer sample needed to include a given weight percent of the total copolymer sample, which is obtained by excluding equal weight fractions from both ends of the distribution. The deviation need not be symmetrical. When expressed as a single number, for example 15% Inter-CD, it shall mean the larger of the positive or negative deviations. For example, for a Gaussian compositional distribution, 95.5% of the polymer is within 20 wt. % ethylene of the mean if the standard deviation is 10%. The Inter-CD for 95.5 wt. % of the polymer is 20 wt. % ethylene for such a sample.
b. Intra-CD is the compositional variation, in terms of ethylene, within a copolymer chain. It is expressed as the minimum difference in weight (wt.) % ethylene that exists between two portions of a single copolymer chain, each portion comprising at least 5 weight % of the chain.
c. Molecular weight distribution (MWD) is a measure of the range of molecular weights within a given copolymer sample. It is characterized in terms of at least one of the ratios of weight-average to number-average molecular weight, M.sub.w /M.sub.n, and Z-average to weight-average molecular weight, M.sub.z /M.sub.w, where: ##EQU1## wherein N.sub.i is the number of molecules of molecular weight M.sub.i.
d. Viscosity Index (V.I.) is the ability of a lubricating oil to accommodate increases in temperature with a minimum decrease in viscosity. The greater this ability, the higher the V.I.
Ethylene-propylene copolymers, particularly elastomers, are important commercial products, and are widely used as viscosity modifiers (VM) in lubricating oils. There exists a continuing need for discovering polymers with unique properties and compositions for use as viscosity modifiers for lubricating oils.
A motor oil should not be too viscous at low temperatures so as to avoid serious frictional losses, facilitate cold starting and provide free oil circulation right from engine startup. On the other hand, it should not be too thin at working temperatures so as to avoid excessive engine wear and excessive oil consumption. It is most desirable to employ a lubricating oil which experiences the least viscosity change with changes in temperature.
Polymeric additives have been extensively used in lubricating oil compositions to impart desirable viscosity-temperature characteristics to the compositions. For example, lubricating oil compositions which use ethylene-propylene copolymers (EPM) or ethylene-propylene-non-conjugated diene terpolymers (EPDM) or, more generally, ethylene-(C.sub.3 -C.sub.18 alpha-olefin copolymers, as V.I. improvers are well known. These additives are designed to permit lubricating oil formulation so that changes in viscosity occurring with variations in temperature are kept as small as possible. Lubricating oils containing such polymeric additives tend to maintain their viscosity at high temperature while at the same time maintaining desirable low viscosity at engine starting temperatures.
Two important properties (although not the only required properties as is known) of these additives relate to low temperature performance and shear stability. Low temperature performance relates to maintaining low viscosity at very low temperatures, while shear stability relates to the resistance of the polymeric additives to being broken down into smaller chains when subjected to mechanical stress in an engine.
In "Polymerization of ethylene and propylene to amorphous copolymers with catalysts of vanadium oxychloride and alkyl aluminum halides"; E. Junghanns, A. Gumboldt and G. Bier; Makromol. Chem., v. 58 (12/12/62): 18-42 the use of a tubular reactor to produce ethylene-propylene copolymer is disclosed in which the composition varies along the chain length. More specifically, this reference discloses the production in a tubular reactor of amorphous ethylene-propylene copolymers using Ziegler catalysts prepared from a vanadium compound and aluminum alkyl. It is disclosed that at the beginning of the tube ethylene is preferentially polymerized, and if no additional make-up of the monomer mixture is made during the polymerization the concentration of monomers changes in favor of propylene along the tube. It is further disclosed that since these changes in concentrations take place during chain propagation, copolymer chains are produced which contain more ethylene on one end than at the other end. It is also disclosed that copolymers made in a tube are chemically non-uniform, but fairly uniform as regards molecular weight distribution. Using the data reported in their FIG. 17 for copolymer prepared in the tube it was estimated that the M.sub.w /M.sub.n ratio for this copolymer was 1.6, and from their FIG. 18, that the intermolecular compositional dispersity (Inter-CD, explained in detail below) of this copolymer was greater than 15%.
J. F. Wehner, "Laminar Flow Polymerization of EPDM Polymer", ACS Symposium Series 65, pp. 140-152 (1978) discloses the results of computer simulation work undertaken to determine the effect of tubular reactor solution polymerization with Ziegler catalysts on the molecular weight distribution of the polymer product. The specific polymer simulated was an elastomeric terpolymer of ethylene-propylene-1,4-hexadiene. On page 149, it is stated that since the monomers have different reactivities, a polymer of varying composition is obtained as the monomers are depleted. However, whether the composition varies inter-or intramolecularly is not distinguished. In Table III on page 148, various polymers having M.sub.w /M.sub.n of about 1.3 are predicted. In the third paragraph on page 144, it is stated that as the tube diameter increases, the polymer molecular weight is too low to be of practical interest, and it is predicted that the reactor will plug. It is implied in the first paragraph on page 149 that the compositional dispersity produced in a tube would be detrimental to product quality.
U.S. Pat. No. 3,681,306 to Wehner is drawn to a process for producing ethylene/higher alpha-olefin copolymers having good processability, by polymerization in at least two consecutive reactor stages. According to this reference, this two-stage process provides a simple polymerization process that permits tailor-making ethylene/alpha-olefin copolymers having predetermined properties, particularly those contributing to processability in commercial applications such as cold-flow, high green strength and millability. According to this reference, the inventive process is particularly adapted for producing elastomeric copolymers, such as ethylene/propylene/5-ethylidene-2-norbornene, using any of the coordination catalysts useful for making EPDM. The preferred process uses one tubular reactor followed by one pot reactor. However, it is also disclosed that one tubular reactor could be used, but operated at different reaction conditions to simulate two stages. As is seen from column 2, lines 14-20, the inventive process makes polymers of broader MWD than those made in a single stage reactor. Although intermediate polymer from the first (pipeline) reactor is disclosed as having a ratio of M.sub.w /M.sub.n of about 2, as disclosed in column 5, lines 54-57, the final polymers produced by the inventive process have an M.sub.w /M.sub.n of 2.4 to 5.
U.S. Pat. No. 3,625,658 to Closon discloses a closed circuit tubular reactor apparatus with high recirculation rates of the reactants which can be used to make elastomers of ethylene and propylene. With particular reference to FIG. 1, a hinged support 10 for vertical leg 1 of the reactor allows for horizontal expansion of the bottom leg thereof and prevents harmful deformations due to thermal expansions, particularly those experienced during reactor clean out.
U.S. Pat. No. 4,065,520 to Bailey et al. discloses the use of a batch reactor to make ethylene copolymers, including elastomers, having broad compositional distributions. Several feed tanks for the reactor are arranged in series, with the feed to each being varied to make the polymer. The products made have crystalline to semi-crystalline to amorphous regions and gradient changes in between. The catalyst system can use vanadium compounds alone or in combination with titanium compound and is exemplified by vanadium oxy-tri-chloride and diisobutyl aluminum chloride. In all examples titanium compounds are used. In several examples hydrogen and diethyl zinc, known transfer agents, are used. The polymer chains produced have a compositionally disperse first length and uniform second length. Subsequent lengths have various other compositional distributions.
In "Estimation of Long-Chain Branching in Ethylene-Propylene Terpolymers from Infinite-Dilution Viscoelastic Properties"; Y. Mitsuda, J. Schrag, and J. Ferry; J. Appl. Pol. Sci., 18, 193 (1974) narrow MWD copolymers of ethylene-propylene are disclosed. For example, in Table II on page 198, EPDM copolymers are disclosed which have M.sub.w /M.sub.n of from 1.19 to 1.32.
In "The Effect of Molecular Weight and Molecular Weight Distribution on the Non-Newtonian Behavior of Ethylene-Propylene-Diene Polymers"; Trans. Soc. Rheol., 14, 83 (1970); C. K. Shih, a whole series of compositionally homogenous fractions were prepared and disclosed. For example, the data in Table I discloses polymer Sample B having a high degree of homogeneity. Also, based on the reported data, the MWD of the sample is very narrow. However, the polymers are not disclosed as having intramolecular dispersity.
U.S. Pat. No. 4,540,753 to Cozewith et al. relates to narrow molecular weight distribution copolymers of ethylene and at least one other alpha-olefin monomer which copolymer is intramolecularly heterogeneous and intermolecularly homogeneous. The copolymers are disclosed to be useful in lubricating oils as viscosity index improvers. The MWD of the copolymers are characterized by at least one of M.sub.w /M.sub.n of less than 2 and M.sub.z /M.sub.w of less than 1.8. The copolymers are preferably made in a tubular reactor, and the patentee discloses that various copolymer structures can be prepared by adding additional monomer(s) during the course of the polymerization. In FIG. 4 thereof (wherein wt. % ethylene at a point on the chain contour versus fractional length along chain contour is plotted), a series of polymer contours are depicted, employing multiple feeds of ethylene along the tube in a tubular reactor.
U.S. Pat. No. 4,135,044 to Beals relates to production of polyethylene by polymerization of ethylene alone or with comonomers and/or telogens in an elongated tubular reactor having an inlet and outlet and a plurality of reaction zones followed by cooling zones wherein a monomer sidestream is introduced at least after the first and second reaction zones.
U.S. Pat. No. 3,035,040 to Findlay relates to a multistage 1-olefin polymerization process wherein catalyst, olefin and diluent are continuously introduced into a small diameter highly elongated tubular reaction zone, and passing the effluent therefrom to a stirred reactor (or a series of stirred reactors). Unreacted olefin and diluent recovered from the second stage polymerization can be recycled to the tubular zone, and multipoint addition of recycled diluent can be employed for additional temperature control in the elongated reaction zone. The patentee employs streamline or plug-flow like (viz, turbulent) conditions in the tubular reactor to improve catalyst efficiency and to avoid the removal of substantial amounts of unused catalyst from this reactor's effluent as in the case of turbulent flow conditions in the tubular reactor.
U.S. Pat. No. 3,162,620 to Gladding relates to ethylene homopolymers and copolymers which are prepared in the form of a coherent film at a quiescent liquid catalyst surface.
Representative publications dealing with ethylene-alpha-olefin copolymers as lubricating oil additives and other uses are as follows:
U.S. Pat. No. 3,378,606 to Kontos relates to semicrystalline/stereoblock copolymers (having crystallinity content of from 4 to 40 percent) having plastic-rubber properties and comprising alternating blocks. The alternating blocks are recited combinations of crystalline, semicrystalline, crystallizable and amorphous homopolymers and copolymers. U.S. Pat. No. 3,853,969 to Kontos relates to crystallizable stereoblock rubbery copolymers having at least three successive and alternating blocks of, e.g., ethylene-propylene amorphous non-crystallizable atactic copolymer and C.sub.2 to C.sub.12 1-olefin crystallizable homopolymer.
U.S. Pat. No. 3,380,978 to Ryan et al. relates to a series, two-stage continuous coordination process wherein alpha-olefin is converted in a first stage (which can be accomplished in a short holdup tubular reactor) to a high molecular weight fraction having a broad molecular weight distribution, after which the polymer, remaining catalyst and unconverted monomer are passed directly into a second polymerization zone (a longer holdup, constant environment autoclave reactor) wherein is formed a lower molecular weight fraction having a narrower molecular weight distribution.
U.S. Pat. No. 3,389,087 to Kresge et al. discloses lubricants containing ethylene-alpha-olefin polymers having a microstructure characterized by a high degree of head-to-head linkages of the alpha-olefin. Preferred copolymers exhibit a degree of crystallinity of up to about 25%.
U.S. Pat. No. 3,522,180 discloses copolymers of ethylene and propylene having a number-average molecular weight of 10,000 to 40,000 and a propylene content of 20 to 70 mole percent as V.I. improvers in lube oils. The preferred M.sub.w /M.sub.n of these copolymers is less than about 4.0.
U.S. Pat. No. 3,551,336 to Jacobson et al. discloses the use of ethylene copolymers of 60-80 mole % ethylene, having no more than 1.3 Wt % of a polymer fraction which is insoluble in normal decane at 55.degree. C. as an oil additive. Minimization of this decane-insoluble fraction in the polymer reduces the tendency of the polymer to form haze in the oil, which haze is evidence of low temperature instability probably caused by adverse interaction with pour depressant additives. The M.sub.w /M.sub.n of these copolymers is "surprisingly narrow" and is less than about 4.0, preferably less than 2.6, e.g., 2.2.
U.S. Pat. No. 3,691,078 to Johnston et al. discloses the use of ethylene-propylene copolymers containing 25-55 wt. % ethylene which have a pendent index of 18-33 and an average pendent size not exceeding 10 carbon atoms as lube oil additives. The M.sub.w /M.sub.n is less than about 8. These additives impart to the oil good low temperature properties with respect to viscosity without adversely affecting pour point depressants.
U.S. Pat. No. 3,697,429 to Engel et al. discloses a blend of ethylene-propylene copolymers having different ethylene contents, i.e., a first copolymer of 40-83 wt. % ethylene and M.sub.w /M.sub.n less than about 4.0 (preferably less than 2.6, e.g. 2.2) and a second copolymer of 3-70 wt. % ethylene and M.sub.w /M.sub.n less than 4.0, with the content of the first differing from the second by at least 4 wt. % ethylene. These blends, when used as V.I. improvers in lubricating oils, provide suitable low temperature viscosity properties with minimal adverse interaction between the lube oil pour depressant and the ethylene-propylene copolymer.
U.S. Pat. No. 3,798,288 to McManimie et al. relates to a method for preparing ethylene-propylene copolymers (which are purported to be "block" copolymers) which comprises alternately polymerizing one of the monomers and mixtures of the monomers in the presence of a vanadium halide/aluminum alkyl compound catalyst system. The polymer is characterized by alternating "blocks" of ethylene-propylene copolymer (the "heteropolymer") with ethylene (or propylene) homopolymer "blocks". A long chain of the homopolymer is followed by a long chain of heteropolymer, and this pattern can be repeated until the desired molecular weight of the copolymer is obtained. Polymerizations are performed in a stirred reactor provided with two electrically driven turbines.
U.S. Pat. No. 3,879,494 to Milkovitch et al. relates to polyblends of chemically joined, phase separated thermoplastic graft copolymers prepared using macromonomers and characterized by a backbone and linear sidechains. The sidechains are prepared by living polymerization followed by termination by reaction with a halogen-containing compound containing a polymerizable moiety. The terminated living polymers, having a narrow molecular weight distribution (M.sub.w /M.sub.n &lt;1.1), are then copolymerized with a second monomer(s) during formation of the graft polymer's backbone. The sidechains can comprise ethylene and lower alpha-olefins (although C.sub.4 to C.sub.12 conjugated dienes and certain vinyl-substituted aromatic hydrocarbons are preferred), and the second monomers can comprise alpha-olefins and comonomers comprising at least one vinylidene group and certain conjugated and non-conjugated dienes.
U.S. Pat. No. 4,254,237 to Shiga et al. is directed to propylene-ethylene copolymers (also purported to be "block" polymers) prepared by a three-step polymerization technique, wherein the ethylene/propylene monomer ratios (and the percents of total polymerization amount) of the three steps are 6/94 or less (60-95 wt. %), 15/85 to 79/21 (1-20 wt. %) and 50/50 to 89/11 (4-35 wt. %) in Steps 1, 2 and 3, respectively, with the ethylene/propylene reaction ratio in the third step being larger than in the second step. Polymerizations are accomplished using titanium trichloride and an organo-aluminum compound catalyst system. U.S. Pat. No. 4,337,326 also to Shiga et al. contains a similar disclosure, and its three step ethylene/propylene monomer ratios (and percents of total polymerization amount) are 6/94 or less (60-95 wt. %), 25/74-67/33 (1-20 wt. %) and 76/24-89/11 (4-35 wt. %) in steps 1, 2 and 3, respectfully, wherein in the steps 2 and 3 ethylene alone is supplied, thereby gradually decreasing the amount of propylene in the polymerization system from the first to the succeeding steps.
U.S. Pat. No. 4,414,369 to Kuroda et al. relates to a continuous process for preparing polyolefins (from C.sub.2 to C.sub.6 olefins) having widely distributed molecular weights in a multi-stage polymerization wherein relatively high molecular weight polymers are first formed, followed to form relatively low molecular weight polymers.
U.S. Pat. No. 4,480,075 to Willis relates to block copolymers prepared by a Ziegler-Natta type polymerization followed by conventional anionic polymerization. The patentee teaches that block copolymers with precise segmented structure which can be obtained with the long-lived anionic systems is not possible with the Ziegler-Natta catalysts because sequential copolymers of the olefin type are swamped with large amounts of the corresponding homopolymers. The patentee indicates that this difficulty stems from the very short average life of nascent chains in Ziegler-Natta catalysis, primarily due to transfer reactions.
U.S. Pat. No. 4,499,242 to Loontjens relates to thermoplastic propylene block copolymers comprising one or more substantially crystalline polypropylene blocks and one or more 1-alkene-propylene copolymer blocks. Diene units are present in at least one of the 1-alkene-propylene copolymer blocks.
U.S. Pat. No. 4,507,515 to Johnston et al. relates to ethylene-alpha-olefin copolymers useful as improving the low temperature viscosity and pumpability properties of lubricating oil comprised of a major and minor component each of which have a defined ethylene sequence distribution with respect to the number of ethylenes in sequences of 3 or more and the percent of ethylene sequences of 3 or more ethylene units. The major and minor polymer components are discrete polymers which can be prepared in separate reaction processes and blended, or can be prepared in situ in the same reaction process.
U.S. Pat. No. 4,575,574 to Kresge et al. (and its divisional U.S. Pat. No. 4,666,619) relates to ethylene ter- or tetrapolymers useful as a viscosity modifier and to a process for preparing the polymer. The patent discloses that either a continuous flow stirred tank reactor or a tubular rector can be employed.
U.S. Pat. No. 4,620,048 to Ver Strate et al. discloses fluid solutions of polydispersed polymers having improved resistance to mechanical shear.
European Patent Application No. 60,609 to Oda et al. relates to ethylene/alpha-olefin copolymers containing 30 to 90 mole % ethylene and having a Q value (M.sub.w /M.sub.n) of not more than 3 and Z value of from 15 to 200. (The Z value is defined as the ratio of the maximum value of the molecular weight to the minimum value of the molecular weight, as measured by gel-permeation chromatography.) The copolymer is disclosed to be useful as a synthetic lubricant oil or fuel component, have number-average molecular weights of 300 to 30,000, and are formed by a continuous polymerization by feeding the catalyst components, the olefin monomers, hydrogen and optionally an intermediate to the polymerization system.
European Patent Application No. 59,034 to Horada et al. is directed to a process for producing copolymers of ethylene with alpha-olefins (and ethylene/alpha-olefin/polyene terpolymers) wherein two polymerization reactors are employed in series and are operated at different temperature levels. The polymers are disclosed to have excellent processability.
Y. Doi et al., "Block Copolymerization of Propylene and Ethylene with the 'Living' Coordination Catalyst V (acac).sub.3 /Al(C.sub.2 H.sub.5).sub.2 Cl/Anisole", pgs. 225-229, Makromol. Chem. Rapid Commun. Vol. 3 (1982) discloses the preparation of P-R and P-R-P block copolymers of syndiotactic propylene blocks (P) and ethylene-propylene random copolymer blocks (R) of narrow M.sub.w /M.sub.n ratios (1.22 to 1.24).
G. C. Evens, "'Living' Coordination Polymerization", 1981 Michigan Molecular Institute on Transition Metal Catalyzed Polymerizations: Unsolved Problems, pp. 245-265 (1981), also relates to attempts to prepare narrow MHD w/M.sub.n ratio (1.5-1.8) copolymers consisting of syndiotactic polypropylene blocks and an ethylene propylene rubber block (PP--EPM--PP). When the living polymerization was initiated with small amounts of propylene (very short first "P" block), the M.sub.w /M.sub.n of the resulting P--R--P block copolymer was reported to be broader (i.e., 2.1; Table III).